usb: dwc2: fix hang during suspend if set as peripheral

usb: dwc2: fix hang during suspend if set as peripheral

dwc2 on most platforms needs phy controller, clock and power supply.
All of them must be enabled/activated to properly operate. If dwc2
is configured as peripheral mode, then all the above three hardware
resources are disabled at the end of the probe:

	/* Gadget code manages lowlevel hw on its own */
	if (hsotg->dr_mode == USB_DR_MODE_PERIPHERAL)
		dwc2_lowlevel_hw_disable(hsotg);

But the dwc2_suspend() tries to read the dwc2's reg to check whether
is_device_mode or not, this would result in hang during suspend if dwc2
is configured as peripheral mode.

Fix this hang by bypassing suspend/resume if lowlevel hw isn't
enabled.

Fixes: 09a75e857790 ("usb: dwc2: refactor common low-level hw code to platform.c")
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Link: https://patch.msgid.link/20251104002503.17158-3-jszhang@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>